Various drowsy driving preventing apparatuses are proposed. In one apparatus proposed in JP 7-232571A, for instance, the apparatus detects drowsiness or sleepiness of a vehicle driver based on behavior of the driver while driving a vehicle, and cautions the driver for a safety driving.
Specifically, a wheel gripping pressure applied to a steering wheel of a vehicle by a vehicle driver and a position of application of such a wheel gripping pressure are detected. A seating pressure applied to a driver seat of the vehicle by the driver and a position of exertion of such a seating pressure are detected. Some flavor is provided to stimulate the driver, when the position of application of the wheel gripping pressure changes to or more times per hour. Air pressure of the driver seat is varied to stimulate the driver, when the seating pressure changes 50% or more and the position of application of the seating pressure changes two or more times per hour. A buzzing sound is provided to stimulate the driver, when the wheel gripping pressure changes 50% or more from a normal condition.
In the above apparatus, the wheel gripping pressure cannot be detected, if the driver fails to grip the steering wheel for some reason. Further, the seating pressure largely varies from person to person. It is therefore difficult to accurately detect the drowsiness of sleepiness of a driver.
As an alternative method for detecting drowsiness of a driver, it is proposed to use biometric information such as a heart rate or a pulse rate to detect the drowsiness. It is however become necessary to have a comparison reference data about degree of drowsiness. This reference data must be pre-stored as a heart rate or a pulse rate in the awakened condition of a driver. Alternatively the reference data must be set by sampling the heart rate or the pulse rate immediately after the driver gets in the vehicle.
Pre-storing of the reference data requires the identification of each driver so that the reference data may be set for the specific driver. Sampling of the heart rate or the pulse rate for setting the reference data requires some time. Further the sampling should be started only after the heart rate and the pulse rate become stable, because the heart rate and the pulse rate varies with the behavior of the driver before getting in the vehicle.